Motor control device

ABSTRACT

A motor control device includes: an X-axis detector; a Y-axis detector; a trajectory command generator that outputs a first position command and a second position command; an X-axis response correction unit that outputs a corrected position command; an X-axis position control unit that generates a first torque command; a Y-axis position control unit that generates a second torque command; a Y-axis measuring instrument that detects second machine end displacement; a Y-axis zero-point estimation unit that extracts characteristics of a zero point of a transfer function on the basis of the second torque command and the machine end displacement or on the basis of the second position command and the machine end displacement; and a response-correction-parameter determination unit that sets a response correction filter by using the characteristics of the zero point.

FIELD

The present invention relates to a motor control device.

BACKGROUND

In recent years, in a machine tool represented by an NC machine tool anda robot represented by an industrial robot, it has been desired torealize highly accurate trajectory control while performing high speedand high acceleration/deceleration driving in order to improve machiningefficiency and production efficiency of the machine tool and the robot.In the machine tool and the robot, it is desired to achieve highacceleration/deceleration driving because of the reason described above.However, only by realizing high responsiveness in a position controlsystem on each axis, a transfer function from a command to a position ata machine end on each axis cannot be matched with each other; and thetrajectory of the machine end becomes distorted with respect to acommand of a curved trajectory.

In Patent Literature 1 as a known example, there is a technique ofreducing vibrations at a tool end during high acceleration/decelerationdriving when designing a controller with taking into consideration ofmechanical resonance for positioning control on a single axis. Further,in Patent Literature 2 as another example, a technique is disclosed inwhich synchronization performance with characteristics of the transferfunction on each axis is improved to be made substantially identical, byexecuting feed forward control after converting a command value by ahigh-cut filter, of which frequency is set lower than that of a servoband of a position control loop on any axis in order to compensate aresponse delay with respect to a command value of a controlled amountsuch as position, speed, and acceleration.

CITATION LIST Patent Literatures

Patent Literature 1: Japanese Patent Application Laid-open No. H8-23691

Patent Literature 2: Japanese Patent Application Laid-open No.2000-339032

SUMMARY Technical Problem

However, according to the techniques described above, if theresponsiveness of a machine having low rigidity is improved to drive themachine at high acceleration/deceleration, transitional changes occurwith respect to the command on each axis due to differences of thetransfer functions on each axis, resulting from the low rigidity of themechanical system, even if the response on each axis is made at a highspeed. Therefore, a problem that the trajectories become distortedoccurs. Particularly, when machining is performed by a machine tool or arobot with reciprocating operations on a symmetrical trajectory, theinfluence of an error caused by such distortions become large, therebycausing damage on a machining surface or a decrease in machiningaccuracy.

The present invention has been achieved in view of the above problems,and an objective of the present invention is to provide a motor controldevice that can execute highly accurate trajectory control even on acontrol target that is configured by a low-rigidity mechanical system.

Solution to Problem

To solve the above problems and achieve the object, the presentinvention relates to a motor control device that controls a first motorcoupled to a first load machine in a first control target and thatcontrols a second motor coupled to a second load machine in a secondcontrol target. The motor control device includes a first detector thatdetects a position of the first motor; a second detector that detects aposition of the second motor; a trajectory command generator thatoutputs a first position command that is a position command for thefirst control target and a second position command that is a positioncommand for the second control target; a response correction unit thatcarries out a calculation to apply a response correction filter to thefirst position command from the trajectory command generator so as tooutput a corrected position command; a first position control unit thatreceives the corrected position command from the response correctionunit and a position detected by the first detector so as to generate afirst torque command such that the position detected by the firstdetector matches the corrected position command; a second positioncontrol unit that receives the second position command from thetrajectory command generator and a position detected by the seconddetector so as to generate a second torque command such that theposition detected by the second detector matches the second positioncommand; a measuring instrument that detects machine end displacement ofthe second load machine in the second control target; a zero-pointestimation unit that extracts characteristics of a zero point of atransfer function from the second torque command to the machine enddisplacement on the basis of the second torque command and the machineend displacement or on the basis of the second position command and themachine end displacement; and a response-correction-parameterdetermination unit that sets the response correction filter of theresponse correction unit by using the characteristics of the zero pointextracted by the zero-point estimation unit. A first torque commandgenerated by the first position control unit is input to the firstmotor, and a second torque command generated by the second positioncontrol unit is input to the second motor.

Advantageous Effects of Invention

According to the present invention, it is feasible to obtain a motorcontrol device that can execute highly accurate trajectory control evenfor a control target that is configured by a low-rigidity mechanicalsystem.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a configuration of a motorcontrol device according to a first embodiment.

FIG. 2 is a block diagram illustrating the relation between a commandtrajectory and an actual trajectory drawn by a tool tip part in themotor control device according to the first embodiment.

FIG. 3 is an example, for comparative purposes of the motor controldevice according to the first embodiment, in which is illustrated a Bodediagram of transfer functions on an X axis and on a Y axis in a statewhere an X-axis response correction unit and a Y-axis responsecorrection unit are not applied.

FIG. 4 is a Bode diagram of transfer functions on an X axis and on a Yaxis in a state where the X-axis response correction unit and the Y-axisresponse correction unit are applied to the motor control deviceaccording to the first embodiment.

FIG. 5 is a block diagram illustrating a configuration of a motorcontrol device according to a second embodiment.

FIG. 6 is a block diagram illustrating a configuration of a motorcontrol device according to a third embodiment.

FIG. 7 is a block diagram illustrating a configuration of a motorcontrol device according to a fourth embodiment.

FIG. 8 is a block diagram illustrating a configuration of a motorcontrol device according to a fifth embodiment.

FIG. 9 is a diagram illustrating a frequency-response display unitprovided in the configuration of the motor control device according tothe fifth embodiment.

DESCRIPTION OF EMBODIMENTS

Exemplary embodiments of a motor control device according to the presentinvention will be explained below in detail with reference to theaccompanying drawings. The present invention is not limited to theembodiments.

First Embodiment

FIG. 1 is a block diagram illustrating a configuration of a motorcontrol device according to a first embodiment of the present invention.In the motor control device according to the present invention, highlyaccurate trajectory control is executed. The trajectory control, here,is to execute control by causing a trajectory of a tool tip part or agriping unit of a robot to follow a curve of a command by moving inmultiple axes, i.e., two or more axes, simultaneously. The trajectory,here, refers to a line connecting positions occupied in a space by thetool tip part configured from a plurality of movable axes as it moves.In a case where the movable axes are constituted by two axes, i.e., an Xaxis that is a first axis and a Y axis that is a second axis, thecommand trajectory and the actual position trajectory drawn by the tooltip part are drawn on a two-dimensional plane as illustrated in FIG. 2.In FIG. 2, the command trajectory is indicated by a solid line and theactual trajectory is indicated by a dotted line.

A trajectory command generator 1 outputs an X-axis position commandsignal and a Y-axis position command signal as position command signalsfor the X axis and the Y axis, respectively. An X-axis responsecorrection unit 13 corrects the X-axis position command signal from thetrajectory command generator 1 by using a response correction filterG_(xrc)(s), and it outputs the corrected X-axis position command to anX-axis position control unit 11. A Y-axis response correction unit 23corrects the Y-axis position command signal from the trajectory commandgenerator 1 by using a response correction filter G_(yrc)(s), and itoutputs the corrected Y-axis position command to a Y-axis positioncontrol unit 21. Characteristics of the response correction filtersG_(xrc)(s) and G_(yrc)(s) are determined by aresponse-correction-parameter determination unit 2, which is describedlater.

An X-axis control target 12 is constituted by an X-axis motor 12 a, anX-axis detector 12 c attached to the X-axis motor 12 a, and an X-axisload machine 12 b coupled to the X-axis motor 12 a. The X-axis controltarget 12 is driven by the X-axis motor 12 a, which generates torquecorresponding to an X-axis torque command T1. An X-axis measuringinstrument 14 is attached to the X-axis control target 12 and measures adisplacement signal of any of the position, speed, and acceleration of amachine end of the X-axis load machine 12 b, which corresponds to thetool tip part. In the following descriptions, the displacement signal,which is an acceleration, is described as “X-axis machine-enddisplacement signal a1”.

The X-axis position control unit 11 outputs the X-axis torque command T1to the X-axis motor 12 a by carrying out a calculation of PID control ortwo-degree-of-freedom control on the basis of the input corrected X-axisposition command and a position detection value detected by the X-axisdetector 12 c. This is done such that the position of the X-axis motor12 a accurately follows the time-varying corrected X-axis positioncommand output from the X-axis response correction unit 13 withoutvibrations.

A Y-axis control target 22 is constituted by a Y-axis motor 22 a, aY-axis detector 22 c attached to the Y-axis motor 22 a, and a Y-axisload machine 22 b coupled to the Y-axis motor 22 a. The Y-axis controltarget 22 is driven by the Y-axis motor 22 a, which generates torquecorresponding to a Y-axis torque command T2. A Y-axis measuringinstrument 24 is attached to the Y-axis control target 22 so as tomeasure the displacement signal of any of the position, speed, andacceleration of a machine end of the Y-axis load machine 22 bcorresponding to the tool tip part. In the following descriptions, thedisplacement signal which is an acceleration and is described as “Y-axismachine-end displacement signal a2”.

The Y-axis position control unit 21 outputs the Y-axis torque command T2to the Y-axis motor 22 a by carrying out a calculation of PID control ortwo-degree-of-freedom control on the basis of the input corrected Y-axisposition command and a position detection value detected by the Y-axisdetector 22 c. This is done such that the position of the Y-axis motor22 a accurately follows the time-varying corrected Y-axis positioncommand output from the Y-axis response correction unit 23 withoutvibrations.

With respect to the X-axis position control unit 11 and the Y-axisposition control unit 21, a control parameter is set respectively suchthat a response delay from the corrected X-axis position command to aposition of the X-axis machine end represented by double integration ofthe X-axis machine-end displacement signal a1, which is acceleration,and a response delay from the corrected Y-axis position command to aposition of the Y-axis machine end represented by double integration ofthe Y-axis machine-end displacement signal a2, which is acceleration,are matched with each other. Here, the response delay represents a timedelay with respect to the command when the command changes at a regularvelocity rate. In this manner, when the response delays on the X axisand the Y axis are matched with each other and when the X-axis positioncommand and the Y-axis position command change at a regular velocityrate, then the trajectory drawn by the position of the X-axis machineend and the position of the Y-axis machine end match the trajectorydrawn by the positions of the corrected X-axis position command and thecorrected Y-axis position command, respectively.

An X-axis excitation-signal generation unit 16 generates a signal havingan M-sequence waveform for a time predetermined by an adjustment-startinstruction operation performed by a user when parameter adjustment isperformed for the motor control device according to the presentembodiment, and it adds an M-sequence excitation signal to the X-axistorque command T1 to drive the X-axis motor 12 a, thereby exciting theX-axis control target 12.

Similar to the X-axis excitation-signal generation unit 16, a Y-axisexcitation-signal generation unit 26 generates a signal having anM-sequence waveform for a predetermined time, and it adds an M-sequenceexcitation signal to the Y-axis torque command T2 to drive the Y-axismotor 22 a, thereby exciting the Y-axis control target 22. In this case,the M-sequence excitation signal is a pseudo-white random signal.

An X-axis zero-point estimation unit 15 performs system identificationby using the X-axis torque command T1 at the time of the excitationsignal that is generated by the X-axis excitation-signal generation unit16 and the X-axis machine-end displacement signal a1 that is detected bythe X-axis measuring instrument 14, which are input and output data;estimates a transfer function G_(fax)(s) from the X-axis torque commandT1 to the X-axis machine-end displacement signal a1; and outputs theresult of extracting information on the zero point on the X axis to theresponse-correction-parameter determination unit 2.

A Y-axis zero-point estimation unit 25 performs system identification byusing the Y-axis torque command T2 at the time of the excitation signalthat is generated by the Y-axis excitation-signal generation unit 26 andthe Y-axis machine-end displacement signal a2 that is detected by theY-axis measuring instrument 24, which are input and output data;estimates a transfer function G_(fay)(s) from the Y-axis torque commandT2 to the Y-axis machine-end displacement signal a2; and outputs theresult of extracting information on the zero point on the Y axis to theresponse-correction-parameter determination unit 2.

The response-correction-parameter determination unit 2 determines andsets characteristics of the response correction filter G_(xrc)(s) of theX-axis response correction unit 13 on the basis of the information onthe zero point on the Y axis, and it determines and sets characteristicsof the response correction filter G_(yrc)(s) of the Y-axis responsecorrection unit 23 on the basis of the information on the zero point onthe X axis.

In the system identification by the X-axis zero-point estimation unit15, the X-axis excitation-signal generation unit 16 adds the M-sequenceexcitation signal to the X-axis torque command T1 to excite the X-axiscontrol target 12 and acquires responses of the X-axis torque command T1and the X-axis machine-end displacement signal a1 detected by the X-axismeasuring instrument 14 as data. The transfer function G_(fax)(s) fromthe X-axis torque command T1 to the X-axis machine-end displacementsignal a1 is estimated by using, for example, a least square method onthe input and output data at the time of M-sequence excitation. Afeature of the transfer function G_(fax)(s) from the X-axis torquecommand T1 to the X-axis machine-end displacement signal a1 is describedhere. As it is given that the X-axis machine-end displacement signal a1is assumed to be acceleration of the machine end, the transfer functionG_(fax)(s) is generally approximated by the following expression (1).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack & \; \\{{G_{fax}(s)} = {\frac{1}{J_{x}}\frac{\prod\limits_{j = 1}^{m}\;\left( {{\frac{1}{\omega_{zxj}^{2}}s^{2}} + {2\frac{\zeta_{zxj}}{\omega_{zxj}}s} + 1} \right)}{\prod\limits_{i = 1}^{n}\;\left( {{\frac{1}{\omega_{pxi}^{2}}s^{2}} + {2\frac{\zeta_{pxi}}{\omega_{pxi}}s} + 1} \right)}}} & (1)\end{matrix}$

In this expression, s denotes a Laplace operator; J_(x) denotes aninertia moment of the X-axis control target 12; ω_(pxi) denotes aresonance frequency in an ith mode; ζ_(pxi) denotes a damping ratio ofthe resonance frequency in the ith mode; ω_(zxj) denotes the jthantiresonant frequency, i.e., an absolute value of complex zero; andζ_(zxj) denotes the jth antiresonant characteristic, i.e., the dampingratio of the complex zero.

When it is assumed that a control target is a two-inertia system inwhich the motor and load inertia are linked by a spring or is a multipleinertia system in which a motor and a plurality of inertial loads areserially linked by a spring, and the displacement of the tip partthereof is a machine-end displacement signal, then antiresonance doesnot appear and the degree of the numerator is approximated as 0, i.e.,m=0. However, the actual structure of a machine system is complicated,and an antiresonant zero point may often be included in the transferfunction from the torque generated by the motor to the machine enddisplacement. In this case, is must be assumed that m≧1 when modeling.

The actual machine system is an infinite dimensional system in a precisesense, which, however, may be modeled as such a low dimensional degreemodel that a response thereof can be approximated by using the degree ofthe numerator as m=1 or m=2. If it is given that the numerator of thetransfer function at this time is assumed to be N_(x)(s), then N_(x)(s)is expressed by the following expression (2):

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 2} \right\rbrack & \; \\{{N_{x}(s)} = {\prod\limits_{j = 1}^{m}\;\left( {{\frac{1}{\omega_{zxj}^{2}}s^{2}} + {2\frac{\zeta_{zxj}}{\omega_{zxj}}s} + 1} \right)}} & (2)\end{matrix}$

The X-axis zero-point estimation unit 15 outputs information on the zeropoint, i.e., information on a polynomial expression of the aboveexpression (2), to the response-correction-parameter determination unit2 via the above operation.

The system identification performed by the Y-axis zero-point estimationunit 25 is an operation similar to that in the case of the X axis, inwhich the Y-axis excitation-signal generation unit 26 adds theM-sequence excitation signal to the Y-axis torque command T2 to excitethe Y-axis control target 22, and it acquires responses of the Y-axistorque command T2 and the Y-axis machine-end displacement signal a2detected by the Y-axis measuring instrument 24 as data. The transferfunction G_(fay)(s) from the Y-axis torque command T2 to the Y-axismachine-end displacement signal a2 is estimated by using, for example,the least square method on the input and output data at the time ofM-sequence excitation. The transfer function G_(fay)(s) here isgenerally approximated by the following expression (3):

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 3} \right\rbrack & \; \\{{G_{fay}(s)} = {\frac{1}{J_{y}}\frac{\prod\limits_{j = 1}^{m}\;\left( {{\frac{1}{\omega_{zyj}^{2}}s^{2}} + {2\frac{\zeta_{zyj}}{\omega_{zyj}}s} + 1} \right)}{\prod\limits_{i = 1}^{n}\;\left( {{\frac{1}{\omega_{pyi}^{2}}s^{2}} + {2\frac{\zeta_{pyi}}{\omega_{pyi}}s} + 1} \right)}}} & (3)\end{matrix}$

In this expression, J_(y) denotes an inertia moment of the Y-axiscontrol target 22; ω_(pyi) denotes a resonance frequency in the ithmode; ζ_(pyi) denotes a damping ratio of the resonance frequency in theith mode; ω_(zyj) denotes the jth antiresonant frequency, i.e., anabsolute value of complex zero; and ζ_(zyj) denotes the jth antiresonantcharacteristic, i.e., a damping ratio of the complex zero.

Similar to the case of the X axis described above, the degree of thenumerator may be approximated as m=1 or m=2 also for the Y axis. Giventhat the numerator of the transfer function at this time is assumed tobe N_(y)(s), then N_(y)(s) is represented by the following expression(4).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 4} \right\rbrack & \; \\{{N_{y}(s)} = {\prod\limits_{j = 1}^{m}\;\left( {{\frac{1}{\omega_{zyj}^{2}}s^{2}} + {2\frac{\zeta_{zyj}}{\omega_{zyj}}s} + 1} \right)}} & (4)\end{matrix}$

The Y-axis zero-point estimation unit 25 outputs information on the zeropoint, i.e., information on a polynomial expression of the aboveexpression (4), to the response-correction-parameter determination unit2 with the above operation.

The response-correction-parameter determination unit 2 determines theresponse correction filter G_(xrc)(s) of the X-axis response correctionunit 13 by using the following expression (5), which is expressed byusing the polynomial expression N_(y)(s) of the transfer functionrepresenting the zero point included in the transfer function G_(fay)(s)from the Y-axis torque command T2 to the Y-axis machine-end displacementsignal a2 extracted by the Y-axis zero-point estimation unit 25 and alow-pass filter F(s).

[Expression 5]G _(xrc)(s)=F(s)*N _(y)(s)  (5)

F(s) on the right side in the expression (5) denotes a low-pass filterfor making the response correction filter G_(xrc)(s) to be proper. Thelow-pass filter F(s) decreases frequency components higher than acontrol band, which are part of the X-axis position command signaloutput from the trajectory command generator 1, so as to suppress anabrupt change and to make the X-axis position command signal smooth. Ifthe X-axis position command signal is originally generated as a smoothsignal, F(s) can be equal to 1.

The response-correction-parameter determination unit 2 determines theresponse correction filter G_(yrc)(S) of the Y-axis response correctionunit 23 by using the following expression (6), which is expressed byusing the polynomial expression N_(x)(s) of the transfer functionrepresenting the zero point included in the transfer function G_(fax)(s)from the X-axis torque command T1 to the X-axis machine-end displacementsignal a1 extracted by the X-axis zero-point estimation unit 15 and thelow-pass filter F(s):

[Expression 6]G _(yrc)(s)=F(s)*N _(x)(s)  (6)

F(s) on the right side in the expression (6) denotes the low-passfilter, which is the same as that used in expression (5).

In the X-axis position control unit 11 and the Y-axis position controlunit 21, the fact that the delay times with respect to the commands onthe X axis and the Y axis are made identical to each other means settingthe control parameters of the X-axis position control unit 11 and theY-axis position control unit 21 such that a response delay from thecorrected X-axis position command to the position of the X-axis machineend represented by the double integration of the X-axis machine-enddisplacement signal a1, which is acceleration, and a response delay fromthe corrected Y-axis position command to the position of the Y-axismachine end represented by the double integration of the Y-axismachine-end displacement signal a2, which is acceleration, are matchedwith each other, as described as above.

Therefore, if there is no zero point in the X-axis control target andthe Y-axis control target, the transfer function from the X-axisposition command x_(ref) to the X-axis machine end position x_(a) isrepresented by the following expression (7), where a denominatorpolynomial of the transfer function from x_(ref) to x_(a) is assumed tobe D(s). Because the response delay from the corrected X-axis positioncommand to the X-axis machine-end displacement signal a1 and theresponse delay from the corrected Y-axis position command to the Y-axismachine-end displacement signal a2 are matched with each other, therelation between the Y-axis position command y_(ref) and the Y-axismachine end position y_(a) is represented by the following expression(8).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 7} \right\rbrack & \; \\{{x_{a}(s)} = {\frac{1}{D(s)}{F(s)}{x_{ref}(s)}}} & (7) \\\left\lbrack {{Expression}\mspace{14mu} 8} \right\rbrack & \; \\{{y_{a}(s)} = {\frac{1}{D(s)}{F(s)}{y_{ref}(s)}}} & (8)\end{matrix}$

Furthermore, if there is a zero point in the transfer function from theX-axis torque command T1 to the X-axis machine end position x_(a) and inthe transfer function from the Y-axis torque command T2 to the Y-axismachine end position y_(a), and even if the command responsecharacteristics are changed by changing the characteristics of theposition controller of the X-axis position control unit 11, then thezero point is stored. Therefore, the relation between the X-axisposition command x_(ref) and the X-axis machine end position x_(a) isrepresented by the following expression (9). Further, similar to thecase of the X axis, the relation between the Y-axis position commandy_(ref) and the Y-axis machine end position y_(a) is represented by thefollowing expression (10):

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 9} \right\rbrack & \; \\{{x_{a}(s)} = {\frac{N_{x}(s)}{D(s)}{F(s)}{x_{ref}(s)}}} & (9) \\\left\lbrack {{Expression}\mspace{14mu} 10} \right\rbrack & \; \\{{y_{a}(s)} = {\frac{N_{y}(s)}{D(s)}{F(s)}{y_{ref}(s)}}} & (10)\end{matrix}$

Therefore, if the characteristics of the zero points on the X axis andthe Y axis are different from each other (N_(x)(s)≠N_(y)(s)), thetrajectories by the X-axis machine end position x_(a) and the Y-axismachine end position y_(a) become distorted in a command curve due tothe corrected X-axis position command and the corrected Y-axis positioncommand, which are affected by the zero point. Therefore, correction isrequired such that the curve is not distorted, even if there is a zeropoint in the X-axis control target and the Y-axis control target. As amethod of performing correction described above, an initial approach isto cancel out the zero points N_(x)(s) and N_(y)(s), which appear in theexpressions (9) and (10) described above. In the case where this methodis applied, if an inverse function of N_(x)(s) is set as thecharacteristics of the response correction filter G_(xrc)(s) of theX-axis response correction unit 13 and an inverse function of N_(y)(s)is set as the characteristics of the response correction filterG_(yrc)(s) of the Y-axis response correction unit 23, the response ofthe X-axis machine end position x_(a) with respect to the X-axisposition command x_(ref) and the response of the Y-axis machine endposition y_(a) with respect to the Y-axis position command y_(ref)become identical to each other. This is represented in the followingexpressions (11) and (12) as ideal expressions.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 11} \right\rbrack & \; \\\begin{matrix}{{x_{a}(s)} = {\frac{N_{x}(s)}{D(s)}\frac{1}{N_{x}(s)}{F(s)}{x_{ref}(s)}}} \\{= {\frac{1}{D(s)}{F(s)}{x_{ref}(s)}}}\end{matrix} & (11) \\\left\lbrack {{Expression}\mspace{14mu} 12} \right\rbrack & \; \\\begin{matrix}{{y_{a}(s)} = {\frac{N_{y}(s)}{D(s)}\frac{1}{N_{y}(s)}{F(s)}{y_{ref}(s)}}} \\{= {\frac{1}{D(s)}{F(s)}{y_{ref}(s)}}}\end{matrix} & (12)\end{matrix}$

However, if set as described above, because a filter of a secondaryresonant system is used as the response correction filter on the X axisand the Y axis, then, the torque command and the position of the motorbecome vibrational, even if the machine end positions on the respectiveaxes do not vibrate. Further, if there is an error in the estimation ofthe zero point, the machine end also becomes vibrational. Therefore, itis not appropriate to set the response correction filters on the X axisand the Y axis to cancel out the antiresonant characteristics asdescribed above. Accordingly, in the present embodiment, by theoperation of the response-correction-parameter determination unit 2, thecharacteristic N_(y)(s) of the zero point on the Y axis is assigned tothe response correction filter G_(xrc)(s) of the X-axis responsecorrection unit 13; and the characteristic N_(x)(s) of the zero point onthe X-axis is assigned to the response correction filter G_(yrc)(s) ofthe Y-axis response correction unit 23. At this time, thecharacteristics from the X-axis position command x_(ref) to the X-axismachine end position x_(a) and the characteristics from the Y-axisposition command y_(ref) to the Y-axis machine end position y_(a) arerepresented respectively by the following expressions (13) and (14).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 13} \right\rbrack & \; \\{{x_{a}(s)} = {\frac{N_{x}(s)}{D(s)}{N_{y}(s)}{F(s)}{x_{ref}(s)}}} & (13) \\\left\lbrack {{Expression}\mspace{14mu} 14} \right\rbrack & \; \\{{y_{a}(s)} = {\frac{N_{y}(s)}{D(s)}{N_{x}(s)}{F(s)}{y_{ref}(s)}}} & (14)\end{matrix}$

According to the above configuration, the transfer function from theposition command signal on the X axis to the load machine position onthe X axis and the transfer function from the position command signal onthe Y axis to the load machine position on the Y axis become identicalto each other.

FIG. 3 is a Bode diagram of the transfer functions, with regard to acertain tool machine, on the X axis and on the Y axis in a state wherethe X-axis response correction unit and the Y-axis response correctionunit are not applied. In FIG. 3, the characteristics of the transferfunctions on the X axis and the Y axis are different from each other dueto the influence of the zero points on the respective axes.

FIG. 4 is a Bode diagram of the transfer functions on the X axis and onthe Y axis in a state where the X-axis response correction unit and theY-axis response correction unit are applied in the present invention. InFIG. 4, the transfer functions on the X axis and the Y axis areidentical to each other, as a result that the X-axis response correctionunit and the Y-axis response correction unit are applied.

Because the motor control device according to the present embodimentoperates as described above, transient responses with respect to thecommand on the X axis and the Y axis become identical to each other.Therefore, trajectory control without distortion of response can beexecuted with respect to the command trajectory at a high speed withhigh accuracy, while reducing a trajectory following error with respectto the command trajectory and vibrations even though a curved trajectoryis drawn by a control target having low rigidity. Further, thecircularity that is an index at the time of drawing a circular arc canbe increased.

In the present embodiment, the X-axis zero-point estimation unit 15receives and uses input of the X-axis torque command T1 to estimate thezero point on the X axis. However, the zero point does not change, evenif the characteristics of the X-axis position control unit 11 arechanged. Therefore, the zero point of the transfer function from theX-axis torque command T1 to the X-axis machine-end displacement signala1 can be extracted by using the X-axis position command instead ofusing the X-axis torque command T1. Similarly, in the Y-axis zero-pointestimation unit 25, the Y-axis position command can be used.

In the present embodiment, as the X-axis motor 12 a and the Y-axis motor22 a, any of a DC motor, a permanent-magnet synchronous motor, and aninduction motor can be used; and the motor used is not limited to arotary motor, and a linear motor can be used.

In the present embodiment, a signal, which is provided by the X-axisexcitation-signal generation unit 16 to the X-axis torque command as aninput, is a signal containing various frequency components; and anM-sequence excitation signal, a sine sweep signal, or a random signalcan be used as an input signal, so long as the X-axis load machine 12 bcan be driven at a steady acceleration or more. As a signal which isprovided by the Y-axis excitation-signal generation unit 26 to theY-axis torque command as an input, the M-sequence excitation signal, thesine sweep signal, or the random signal can be used as the input signalsimilar to the case of the X axis. Further, if a machine is providedwith a function of inputting any of the excitation signals describedabove to the X-axis torque command and the Y-axis torque command, theX-axis excitation-signal generation unit 16 and the Y-axisexcitation-signal generation unit 26 may not be provided.

In the present embodiment, the system identification is performed byusing the least square method. However, the method is not limitedthereto, and another method represented by a spectral analysistechnique, a multi-decimation identification method on the basis of anARX model, or other method represented by an MOESP method can be used.

In the present embodiment, the X-axis measuring instrument 14 and theY-axis measuring instrument 24 that respectively detect the X-axismachine-end displacement signal a1 and the Y-axis machine-enddisplacement signal a2 are required only at the time of parameteradjustment. Therefore, the X-axis measuring instrument 14 and the Y-axismeasuring instrument 24 can be made detachable and they may be detachedafter adjustment. That is, the sensor may not be provided when operatedas the motor control device.

As described above, according to the present embodiment, highly accuratetrajectory control can be executed even in a case where the controltarget is configured by a low-rigidity mechanical system. This is doneby setting the response correction unit on each axis by theresponse-correction-parameter determination unit on the basis of thecharacteristics of the zero point on each axis acquired by thezero-point estimation unit and by setting the transfer function from thecommand to the machine end position on each axis to be the same.

Second Embodiment

FIG. 5 is a block diagram illustrating a configuration of a motorcontrol device according to a second embodiment of the presentinvention. In the second embodiment, blocks denoted with reference signsidentical to those of the first embodiment illustrated in FIG. 1 havefunctions equivalent to those of the first embodiment, and redundantdescriptions of the configurations and operations thereof will beomitted.

An X-axis control target 212 is constituted by an X-axis motor 212 a, anX-axis detector 212 c attached to the X-axis motor 212 a, and an X-axisload machine 212 b coupled to the X-axis motor 212 a. The X-axis motor212 a and the X-axis load machine 212 b are coupled to each other withhigh rigidity, and the behavior of the X-axis load machine 212 b isdetected by the X-axis detector 212 c. The X-axis control target 212 isdriven by the X-axis motor 212 a that generates torque on the basis ofthe X-axis torque command T1. As a control target having such rigidity,an NC (Numerical Control) lathe can be mentioned as an example.

With respect to the X-axis position control unit 11 and a Y-axisposition control unit 221, a control parameter, which is used for acontrol calculation of the X-axis position control unit 11 and theY-axis position control unit 221, is set respectively such that aresponse delay from the corrected X-axis position command to a positionof the X-axis machine end represented by double integration of theX-axis machine-end displacement signal a1 that is the acceleration and aresponse delay from the corrected Y-axis position command to a positionof the Y-axis machine end represented by double integration of theY-axis machine-end displacement signal a2 that is the acceleration arematched with each other.

A response-correction-parameter determination unit 202 determines theresponse correction filter G_(xrc)(s) of the X-axis response correctionunit 13 on the basis of the following expression (15), which uses thepolynomial expression N_(y)(s) of the transfer function representing thezero point included in the transfer function G_(fay)(s) from the Y-axistorque command T2 to the Y-axis machine-end displacement signal a2extracted by the Y-axis zero-point estimation unit 25 and the low-passfilter F(s). Similar to the first embodiment, the low-pass filter F(s)on the right side in the following expression (15) decreases frequencycomponents higher than a control band, of the X-axis position commandsignal output from the trajectory command generator 1, to reduce anabrupt change and smooth the X-axis position command signal.

[Expression 15]G _(xrc)(s)=F(s)*N _(y)(s)  (15)

When the rigidity of the X-axis control target 212 is high, the transferfunction G_(fax)(s) from the X-axis torque command T1 to theacceleration of the X-axis machine end is approximated by the followingexpression (16). Here, the acceleration of the X-axis machine end can beacquired by differentiating a detection value of the X-axis detector 212c twice, because the X-axis motor 212 a and the X-axis load machine 212b are coupled to each other with high rigidity. Further, regarding theY-axis control target 22 similar to the first embodiment, if the Y-axismachine-end displacement signal a2 is assumed to be the acceleration ofthe machine end, the transfer function G_(fay)(s) from the Y-axis torquecommand T2 to the Y-axis machine-end displacement signal a2 detected bythe Y-axis measuring instrument 24 is approximated by the followingexpression (17)

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 16} \right\rbrack & \; \\{{G_{fax}(s)} = \frac{1}{J_{x}}} & (16) \\\left\lbrack {{Expression}\mspace{14mu} 17} \right\rbrack & \; \\{{G_{fay}(s)} = {\frac{1}{J_{y}}\frac{\prod\limits_{j = 1}^{m}\;\left( {{\frac{1}{\omega_{zyj}^{2}}s^{2}} + {2\frac{\zeta_{zyj}}{\omega_{zyj}}s} + 1} \right)}{\prod\limits_{i = 1}^{n}\;\left( {{\frac{1}{\omega_{pyi}^{2}}s^{2}} + {2\frac{\zeta_{pyi}}{\omega_{pyi}}s} + 1} \right)}}} & (17)\end{matrix}$

At this time, if a denominator polynomial of the transfer function fromthe X-axis position command x_(ref) to the X-axis machine end positionx_(a) is assumed to be D(s), the transfer function from x_(ref) to x_(a)is represented by the following expression (18) by using the polynomialexpression D(s). Further, the transfer function from the Y-axis positioncommand y_(ref) to the Y-axis machine end position y_(a) is representedby the following expression (19).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 18} \right\rbrack & \; \\{{x_{a}(s)} = {\frac{1}{D(s)}{F(s)}{x_{ref}(s)}}} & (18) \\\left\lbrack {{Expression}\mspace{14mu} 19} \right\rbrack & \; \\{{y_{a}(s)} = {\frac{N_{y}(s)}{D(s)}{F(s)}{y_{ref}(s)}}} & (19)\end{matrix}$

Similar to the first embodiment, the response-correction-parameterdetermination unit 202 does not cancel out the zero point by using theinverse function, but uses a method of assigning the characteristicN_(y)(s) of the zero point on the Y axis to the response correctionfilter G_(xrc)(s) of the X-axis response correction unit 13. At thistime, the characteristics from the X-axis position command x_(ref) tothe X-axis machine end position x_(a) and the characteristics from theY-axis position command y_(ref) to the Y-axis machine end position y_(a)are respectively represented by the following expressions (20) and (21),and the transfer functions on the X axis and the Y axis can be matchedwith each other.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 20} \right\rbrack & \; \\{{x_{a}(s)} = {\frac{1}{D(s)}{N_{y}(s)}{F(s)}{x_{ref}(s)}}} & (20) \\\left\lbrack {{Expression}\mspace{14mu} 21} \right\rbrack & \; \\{{y_{a}(s)} = {\frac{N_{y}(s)}{D(s)}{F(s)}{y_{ref}(s)}}} & (21)\end{matrix}$

Because the motor control device according to the present embodimentoperates as described above, transient responses with respect to thecommand on the X axis and the Y axis become identical to each other.Therefore, trajectory control without distortion of response can beexecuted with respect to the command trajectory at a high speed and withhigh accuracy, while reducing trajectory following errors with respectto the command trajectory and vibrations, even if a curved trajectory isdrawn by a control target having an axis with low rigidity and an axiswith high rigidity. Further, the circularity that is an index at thetime of drawing a circular arc can be increased. When rigidity of oneaxis, of the two axes of the control target, is high, trajectory controlcan be executed with less number of measurement sensors and fewercorrection calculations.

Third Embodiment

FIG. 6 is a block diagram illustrating a configuration of a motorcontrol device according to a third embodiment of the present invention.In the third embodiment, blocks denoted with reference signs identicalto those of the first embodiment illustrated in FIG. 1 have functionsequivalent to those of the first embodiment, and redundant descriptionsof the configurations and operations thereof will be omitted. Asillustrated in FIG. 6, the motor control device according to the thirdembodiment has a configuration in which a Z axis, which is the thirdaxis, is added to the motor control device according to the firstembodiment.

A trajectory command generator 301 outputs an X-axis position commandsignal, a Y-axis position command signal, and a Z-axis position commandsignal, which are position command signals for the X axis, the Y axis,and the Z axis, respectively.

A Z-axis response correction unit 33 corrects the Z-axis positioncommand signal from the trajectory command generator 301 by using aresponse correction filter G_(zrc)(s), and it outputs a corrected Z-axisposition command to a Z-axis position control unit 31. Characteristicsof the response correction filter G_(zrc)(s) are determined by aresponse-correction-parameter determination unit 302 which is describedlater.

A Z-axis control target 32 is constituted by a Z-axis motor 32 a, aZ-axis detector 32 c attached to the Z-axis motor 32 a, and a Z-axisload machine 32 b coupled to the Z-axis motor 32 a. The Z-axis controltarget 32 is driven by the Z-axis motor 32 a that generates torquecorresponding to a Z-axis torque command T3. A Z-axis measuringinstrument 34 is attached to the Z-axis control target 32 to measure adisplacement signal of any of the position, speed, and acceleration of amachine end of the Z-axis load machine 32 b, which corresponds to thetool tip part. In the following descriptions, the displacement signal,which is the acceleration, is described as “Z-axis machine-enddisplacement signal a3”.

The Z-axis position control unit 31 outputs the Z-axis torque command T3to the Z-axis motor 32 a by carrying out a calculation of PID control ortwo-degree-of-freedom control on the basis of the input corrected Z-axisposition command and a position detection value detected by the Z-axisdetector 32 c. This is done such that the position of the Z-axis motor32 a accurately follows the time-varying corrected Z-axis positioncommand output from the Z-axis response correction unit 33 withoutvibrations.

With respect to the X-axis position control unit 11, the Y-axis positioncontrol unit 21, and the Z-axis position control unit 31, a controlparameter is set respectively such that a response delay from thecorrected X-axis position command to the position of the X-axis machineend represented by double integration of the X-axis machine-enddisplacement signal a1 that is the acceleration, a response delay fromthe corrected Y-axis position command to the position of the Y-axismachine end represented by double integration of the Y-axis machine-enddisplacement signal a2 that is the acceleration, and a response delayfrom the corrected Z-axis position command to a position of the Z-axismachine end represented by double integration of the Z-axis machine-enddisplacement signal a3 that is the acceleration are matched with eachother.

A Z-axis excitation-signal generation unit 36 generates a signal havingan M-sequence waveform for a time predetermined by an adjustment-startinstruction operation performed by a user, when parameter adjustment isperformed by the motor control device according to the presentembodiment, and it adds an M-sequence excitation signal to the Z-axistorque command T3 to drive the Z-axis motor 32 a, thereby exciting theZ-axis control target 32.

A Z-axis zero-point estimation unit 35 performs system identification byusing the Z-axis torque command T3 at the time of generating theexcitation signal by the Z-axis excitation-signal generation unit 36 asdescribed above and the Z-axis machine-end displacement signal a3detected by the Z-axis measuring instrument 34, which are input andoutput data; estimates a transfer function G_(faz)(s) from the Z-axistorque command T3 to the Z-axis machine-end displacement signal a3; andoutputs a result of extracting information of the zero point on theZ-axis to the response-correction-parameter determination unit 302.

The response-correction-parameter determination unit 302 determines andsets the characteristics of the response correction filter G_(xrc)(s) ofthe X-axis response correction unit 13 on the basis of the informationof the zero point on the Y axis and the zero point on the Z axis;determines and sets the characteristics of the response correctionfilter G_(yrc)(s) of the Y-axis response correction unit 23 on the basisof the information of the zero point on the X axis and the zero point onthe Z axis; and determines and sets characteristics of the responsecorrection filter G_(zrc)(s) of the Z-axis response correction unit 33on the basis of the information of the zero point on the X axis and thezero point on the Y axis.

In the system identification by the Z-axis zero-point estimation unit35, similar to the case of the X axis and the Y axis described in thefirst embodiment, the Z-axis excitation-signal generation unit 36 addsthe M-sequence excitation signal to the Z-axis torque command T3 toexcite the Z-axis control target 32, and acquires responses of theZ-axis torque command T3 and the Z-axis machine-end displacement signala3 detected by the Z-axis measuring instrument 34 as data. The transferfunction G_(faz)(s) from the Z-axis torque command T3 to the Z-axismachine-end displacement signal a3 is estimated by using, as an example,the least square method with respect to the input and output data at thetime of M-sequence excitation. The characteristics of the transferfunction G_(faz)(s) from the Z-axis torque command T3 to the Z-axismachine-end displacement signal a3 are described here. When the Z-axismachine-end displacement signal a3 is assumed to be the acceleration ofthe machine end, the transfer function G_(faz)(s) is generallyapproximated by the following expression (22).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 22} \right\rbrack & \; \\{{G_{faz}(s)} = {\frac{1}{J_{z}}\frac{\prod\limits_{j = 1}^{m}\;\left( {{\frac{1}{\omega_{zzj}^{2}}s^{2}} + {2\frac{\zeta_{zzj}}{\omega_{zzj}}s} + 1} \right)}{\prod\limits_{i = 1}^{n}\;\left( {{\frac{1}{\omega_{pzi}^{2}}s^{2}} + {2\frac{\zeta_{pzi}}{\omega_{pzi}}s} + 1} \right)}}} & (22)\end{matrix}$

In this expression, J_(z) denotes an inertia moment of the Z-axiscontrol target 32. ω_(pzi) denotes a resonance frequency in the ithmode, ζ_(pzi) denotes a damping ratio of the resonance frequency in theith mode, ω_(zzj) denotes the jth antiresonant frequency, i.e., anabsolute value of complex zero, ζ_(zzj) denotes the jth antiresonantcharacteristic, i.e., a damping ratio of the complex zero.

Similar to the X axis and the Y axis in the above embodiments, thedegree of the numerator may be approximated as m=1 or m=2. When thenumerator of the transfer function at this time is assumed to beN_(z)(s), N_(z)(s) is represented by the following expression (23).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 23} \right\rbrack & \; \\{{N_{z}(s)} = {\prod\limits_{j = 1}^{m}\;\left( {{\frac{1}{\omega_{zzj}^{2}}s^{2}} + {2\frac{\zeta_{zzj}}{\omega_{zzj}}s} + 1} \right)}} & (23)\end{matrix}$

The Z-axis zero-point estimation unit 35 outputs information of the zeropoint, i.e., information of a polynomial expression of the aboveexpression (23) to the response-correction-parameter determination unit302 by the above operation.

The response-correction-parameter determination unit 302 determines theresponse correction filter G_(xrc)(s) of the X-axis response correctionunit 13 on the basis of the following expression (24), which uses thepolynomial expression N_(y)(s) of the transfer function representing thezero point included in the transfer function G_(fay)(s) from the Y-axistorque command T2 to the Y-axis machine-end displacement signal a2extracted by the Y-axis zero-point estimation unit 25; a polynomialexpression N_(z)(s) of the transfer function representing the zero pointincluded in the transfer function G_(faz)(s) from the Z-axis torquecommand T3 to the Z-axis machine-end displacement signal a3 extracted bythe Z-axis zero-point estimation unit 35; and the low-pass filter F(s).

[Expression 24]G _(xrc)(s)=F(s)*N _(y)(s)*N _(z)  (24)

F(s) on the right side in the expression (24) is a low-pass filter formaking the response correction filter G_(xrc) (s) proper. The low-passfilter F(s) decreases frequency components higher than the control band,of the X-axis position command signal output from the trajectory commandgenerator 301, to reduce an abrupt change and smooth the X-axis positioncommand signal. If the X-axis position command signal is originallygenerated smoothly, F(s) can be equal to 1.

The response-correction-parameter determination unit 302 determines theresponse correction filter G_(yrc)(s) of the Y-axis response correctionunit 23 on the basis of the following expression (25), which uses thepolynomial expression N_(x)(s) of the transfer function representing thezero point included in the transfer function G_(fax)(s) from the X-axistorque command T1 to the X-axis machine-end displacement signal a1extracted by the X-axis zero-point estimation unit 15; the polynomialexpression N_(z)(s) of the transfer function representing the zero pointincluded in the transfer function G_(faz)(s) from the Z-axis torquecommand T3 to the Z-axis machine-end displacement signal a3 extracted bythe Z-axis zero-point estimation unit 35; and the low-pass filter F(s).

[Expression 25]G _(yrc)(s)=F(s)*N _(x)(s)*N _(z)(s)  (25)

F(s) on the right side in the expression (25) is the low-pass filterwhich is the same as in the expression (24) described above.

The response-correction-parameter determination unit 302 determines theresponse correction filter G_(zrc)(s) of the Z-axis response correctionunit 33 on the basis of the following expression (26), which uses thepolynomial expression N_(y)(s) of the transfer function representing thezero point included in the transfer function G_(fax)(s) from the X-axistorque command T1 to the X-axis machine-end displacement signal a1extracted by the X-axis zero-point estimation unit 15; the polynomialexpression N_(y)(s) of the transfer function representing the zero pointincluded in the transfer function G_(fay)(s) from the Y-axis torquecommand T2 to the Y-axis machine-end displacement signal a2 extracted bythe Y-axis zero-point estimation unit 25; and the low-pass filter F(s).

[Expression 26]G _(zrc)(s)=F(s)*N _(x)(s)*N _(y)(s)  (26)

F(s) on the right side in the expression (26) is the low-pass filtersame as in the expression (24) described above.

Also in the present embodiment, similar to the first embodiment, in theX-axis position control unit 11, the Y-axis position control unit 21,and the Z-axis position control unit 31, it means that the delay timeswith respect to the commands on the X axis, the Y axis, and the Z axisare made identical to set the control parameters of the X-axis positioncontrol unit 11, the Y-axis position control unit 21, and the Z-axisposition control unit 31, which is described above. This is done suchthat a response delay from the corrected X-axis position command to theX-axis machine-end displacement signal a1, a response delay from thecorrected Y-axis position command to the Y-axis machine-end displacementsignal Y-axis machine-end displacement signal a2, and a response delayfrom the corrected Z-axis position command to the Z-axis machine-enddisplacement signal a3 are matched with each other.

If there is a zero point in the transfer function from the X-axis torquecommand T1 to the X-axis machine end position x_(a), the transferfunction from the Y-axis torque command T2 to the Y-axis machine endposition y_(a), and the transfer function from the Z-axis torque commandT3 to the Z-axis machine end position z_(a), then, the relation betweenthe X-axis position command x_(ref) and the X-axis machine end positionx_(a) is represented by the following expression (27); the relationbetween the Y-axis position command y_(ref) and the Y-axis machine endposition y_(a) is represented by the following expression (28); and therelation between the Z-axis position command z_(ref) and the Z-axismachine end position z_(a) is represented by the following expression(29).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 27} \right\rbrack & \; \\{{x_{a}(s)} = {\frac{N_{x}(s)}{D(s)}{F(s)}{x_{ref}(s)}}} & (27) \\\left\lbrack {{Expression}\mspace{14mu} 28} \right\rbrack & \; \\{{y_{a}(s)} = {\frac{N_{y}(s)}{D(s)}{F(s)}{y_{ref}(s)}}} & (28) \\\left\lbrack {{Expression}\mspace{14mu} 29} \right\rbrack & \; \\{{z_{a}(s)} = {\frac{N_{z}(s)}{D(s)}{F(s)}{z_{ref}(s)}}} & (29)\end{matrix}$

Therefore, if the characteristics of the zero points on the X axis, theY axis, and the Z axis are different from each other, i.e.,N_(x)(s)≠N_(y)(s)≠N_(z)(s), the trajectories by the X-axis machine endposition x_(a) and the Y-axis machine end position y_(a) becomedistorted in a command curve by the corrected X-axis position commandand the corrected Y-axis position command due to the influence of thezero point. Therefore, correction is required such that even if there isa zero point in the X-axis control target, the Y-axis control target,and the Z-axis control target, the curve not be distorted. As a methodof performing correction described above, the inverse function is notused due to the reason described in the first embodiment. Insteadthereof, used is a method of assigning the characteristic N_(y)(s) ofthe zero point on the Y axis and the characteristic N_(z)(s) of the zeropoint on the Z axis to the response correction filter G_(xrc)(S) of theX-axis response correction unit 13; assigning the characteristicN_(x)(s) of the zero point on the X axis and the characteristic N_(z)(s)of the zero point on the Z axis to the response correction filterG_(yrc)(s) of the Y-axis response correction unit 23; and assigning thecharacteristic N_(x)(s) of the zero point on the X axis and thecharacteristic N_(y)(s) of the zero point on the Y axis to the responsecorrection filter G_(zrc)(s) of the Z-axis response correction unit 33.At this time, the characteristics from the X-axis position commandx_(ref) to the X-axis machine end position x_(a) is represented by thefollowing expression (30); the characteristics from the Y-axis positioncommand y_(ref) to the Y-axis machine end position y_(a) is representedby the following expression (31); and the characteristics from theZ-axis position command z_(ref) to the Z-axis machine end position z_(a)is represented by the following expression (32). By matching thetransfer characteristics on the X axis, the transfer characteristics onthe Y axis, and the transfer characteristics on the Z axis with eachother, the influences of the zero points are made identical to eachother.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 30} \right\rbrack & \; \\{{x_{a}(s)} = {\frac{N_{x}(s)}{D(s)}{N_{y}(s)}{N_{z}(s)}{F(s)}{x_{ref}(s)}}} & (30) \\\left\lbrack {{Expression}\mspace{14mu} 31} \right\rbrack & \; \\{{y_{a}(s)} = {\frac{N_{y}(s)}{D(s)}{N_{x}(s)}{N_{z}(s)}{F(s)}{y_{ref}(s)}}} & (31) \\\left\lbrack {{Expression}\mspace{14mu} 32} \right\rbrack & \; \\{{z_{a}(s)} = {\frac{N_{z}(s)}{D(s)}{N_{x}(s)}{N_{y}(s)}{F(s)}{z_{ref}(s)}}} & (32)\end{matrix}$

According to the above configuration, the transfer function from theposition command signal on the X axis to the load machine position onthe X axis; the transfer function from the position command signal onthe Y axis to the load machine position on the Y axis; and the transferfunction from the position command signal on the Z axis to the loadmachine position on the Z axis become identical to each other.

Because the motor control device according to the present embodimentoperates as described above, transient responses with respect to thecommand on the X axis, the Y axis, and the Z axis become identical toeach other. Therefore, trajectory control without distortion of responsecan be executed with respect to the command trajectory at a high speedand with high accuracy, while reducing a trajectory-following-error withrespect to the command trajectory and vibrations even though a curvedtrajectory is drawn by a control target having low rigidity.

In the present embodiment, the driving system has a three-axisconfiguration. However, the driving system is not limited thereto, andcan have a multi axes configuration having more than three axes by usingthe same method.

Fourth Embodiment

FIG. 7 is a block diagram illustrating a configuration of a motorcontrol device according to a fourth embodiment of the presentinvention. In the fourth embodiment, blocks denoted with reference signsidentical to those of the first embodiment illustrated in FIG. 1 havefunctions equivalent to those of the first embodiment, and redundantdescriptions of the configurations and operations thereof will beomitted. As illustrated in FIG. 7, the motor control device according tothe fourth embodiment has a configuration in which an X-axismachine-characteristics analysis unit 417, a Y-axismachine-characteristics analysis unit 427, and an automatic-adjustmentdetermination unit 403 are added to the motor control device accordingto the first embodiment.

The X-axis machine-characteristics analysis unit 417 performs conversionfrom a time domain to a frequency domain by using the X-axis torquecommand T1 at the time of generating the excitation signal by the X-axisexcitation-signal generation unit 16 and the X-axis machine-enddisplacement signal a1 detected by the X-axis measuring instrument 14 asinput and output data, and it outputs frequency characteristics on the Xaxis to the automatic-adjustment determination unit 403.

The Y-axis machine-characteristics analysis unit 427 performs conversionfrom the time domain to the frequency domain by using the Y-axis torquecommand T2 at the time of generating the excitation signal by the Y-axisexcitation-signal generation unit 26 and the Y-axis machine-enddisplacement signal a2 detected by the Y-axis measuring instrument 24 asinput and output data; and it outputs frequency characteristics on the Yaxis to the automatic-adjustment determination unit 403.

The automatic-adjustment determination unit 403 detects the presence ofthe antiresonant characteristic on the X axis from the frequencycharacteristics on the X axis output by the X-axismachine-characteristics analysis unit 417; and it outputs theantiresonant characteristic to an X-axis zero-point estimation unit 415,if there is the antiresonant characteristic. Similarly, theautomatic-adjustment determination unit 403 detects the presence of theantiresonant characteristic on the Y axis from the frequencycharacteristics on the Y axis output by the Y-axismachine-characteristics analysis unit 427; and if there is theantiresonant characteristic, it outputs the antiresonant characteristicto a Y-axis zero-point estimation unit 425. Detection of the presence ofthe antiresonant characteristic is performed by using a moving-averagefilter to perform a smoothing process and deriving a minimum point fromthe smoothed frequency characteristics, so that a sketch can beacquired, while reducing fluctuations of minute gain values betweenadjacent frequencies with regard to the acquired frequencycharacteristics.

Upon the output of an operation command from the automatic-adjustmentdetermination unit 403, the X-axis zero-point estimation unit 415performs system identification by using the X-axis torque command T1 atthe time of generating the excitation signal by the X-axisexcitation-signal generation unit 16 and the X-axis machine-enddisplacement signal a1 detected by the X-axis measuring instrument 14,which are input and output data; estimates the transfer functionG_(fax)(s) from the X-axis torque command T1 to the X-axis machine-enddisplacement signal a1; and outputs a result of extracting informationof the zero point on the X axis, i.e., information of the polynomialexpression N_(x)(s) of the transfer function representing the zeropoint, to the response-correction-parameter determination unit 2. If theoperation command is not output from the automatic-adjustmentdetermination unit 403, the following expression (33) is output to theresponse-correction-parameter determination unit 2.

[Expression 33]N _(x)(s)=1  (33)

Upon the output of an operation command from the automatic-adjustmentdetermination unit 403, the Y-axis zero-point estimation unit 425performs system identification by using the Y-axis torque command T2 atthe time of generating the excitation signal by the Y-axisexcitation-signal generation unit 26 and the Y-axis machine-enddisplacement signal a2 detected by the Y-axis measuring instrument 24,which are input and output data; estimates the transfer functionG_(fay)(s) from the Y-axis torque command T2 to the Y-axis machine-enddisplacement signal a2; and outputs a result of extracting informationof the zero point on the Y axis, i.e., information of the polynomialexpression N_(y)(s) of the transfer function representing the zeropoint, to the response-correction-parameter determination unit 2. If theoperation command is not output from the automatic-adjustmentdetermination unit 403, the following expression (34) is output to theresponse-correction-parameter determination unit 2.

[Expression 34]N _(y)(s)=1  (34)

By having the above configuration, even if an axis having low rigidityand an axis having high rigidity are present in the control target,appropriate parameter adjustment can be performed by automaticallydiscriminating the axis having low rigidity and the axis having highrigidity. Specifically, if all the axes have high rigidity, the aboveexpressions (33) and (34) are input to the response-correction-parameterdetermination unit 2. Therefore, if the denominator polynomial of thetransfer function from the X-axis position command x_(ref) to the X-axismachine end position x_(a) is assumed to be D(s), the characteristicfrom the X-axis position command x_(ref) to the X-axis machine endposition x_(a) is represented by the following expression (35) by usingthe low-pass filter F(s).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 35} \right\rbrack & \; \\{{X_{a}(s)} = {\frac{1}{D(s)}{F(s)}{X_{ref}(s)}}} & (35)\end{matrix}$

Similarly, the characteristic from the Y-axis position command y_(ref)to the Y-axis machine end position y_(a) is represented by the followingexpression (36).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 36} \right\rbrack & \; \\{{Y_{a}(s)} = {\frac{1}{D(s)}{F(s)}{Y_{ref}(s)}}} & (36)\end{matrix}$

In this manner, the transfer characteristics on the X axis and thetransfer characteristics on the Y axis can be matched with each other.If rigidity of any axis is low, the relation is the same as that of theX axis and the Y axis in the second embodiment, and the transfercharacteristics on the X axis and the transfer characteristics on the Yaxis can be matched with each other. If rigidity of all the axes is low,the relation is the same as that of the X axis and the Y axis in thefirst embodiment, and the transfer characteristics on the X axis and thetransfer characteristics on the Y axis can be matched with each other.

Because the motor control device according to the present embodimentoperates as described above, even if the rigidity degree of each axis isunknown when a curved trajectory is drawn by a control target having anaxis with low rigidity and an axis with high rigidity mixed therein, theaxis with low rigidity and the axis with high rigidity can beautomatically discriminated to perform appropriate parameter adjustment.Further, the transient responses with respect to the command on the Xaxis and the Y axis become identical to each other. Therefore,trajectory control without distortion of response can be executed withrespect to the command trajectory at a high speed and with highaccuracy, while reducing a trajectory following error with respect tothe command trajectory and vibrations.

In the present embodiment, the driving system has a two-axisconfiguration. However, the configuration of the driving system is notlimited thereto, and can have a multi axes configuration having three ormore axes by using the same method.

Fifth Embodiment

FIG. 8 is a block diagram illustrating a configuration of a motorcontrol device according to a fifth embodiment of the present invention.In the fifth embodiment, blocks denoted with reference signs identicalto those of the first embodiment illustrated in FIG. 1 have functionsequivalent to those of the first embodiment, and redundant descriptionsof the configurations and operations thereof will be omitted. Asillustrated in FIG. 8, the motor control device according to the presentembodiment includes a frequency-response display unit 504 instead of theX-axis zero-point estimation unit 15 and the Y-axis zero-pointestimation unit 25 of the motor control device according to the firstembodiment. The frequency-response display unit 504 includes a firstmonitoring unit 504 a, a second monitoring unit 504 b, and a user inputdevice 504 c. FIG. 9 is a diagram illustrating the frequency-responsedisplay unit 504 provided in the configuration of the motor controldevice according to the fifth embodiment of the present invention.

The first monitoring unit 504 a performs system identification by usingthe X-axis torque command T1 at the time of generating the excitationsignal by the X-axis excitation-signal generation unit 16 and the X-axismachine-end displacement signal a1 detected by the X-axis measuringinstrument 14, which are input and output data, and it displays, on thesame graph, a frequency characteristic F_(rx) from the X-axis torquecommand T1 to the X-axis machine-end displacement signal a1 and afrequency characteristic F_(fax5) of a transfer function G_(fax5)(s)obtained by modeling the frequency characteristic F_(rx) into lowdimensional degree model. In FIG. 9, the frequency characteristic F_(rx)is plotted by a solid line, and the frequency characteristic F_(fax5) isplotted by a dotted line.

The second monitoring unit 504 b performs system identification by usingthe Y-axis torque command T2 at the time of generating the excitationsignal by the Y-axis excitation-signal generation unit 26 and the Y-axismachine-end displacement signal a2 detected by the Y-axis measuringinstrument 24, which are input and output data; and displays, on thesame graph, a frequency characteristic F_(ry) from the Y-axis torquecommand T2 to the Y-axis machine-end displacement signal a2 and afrequency characteristic F_(fay5) of a transfer function G_(fay5)(s)obtained by modeling the frequency characteristic F_(ry) into lowdimensional degree model. In FIG. 9, the frequency characteristic F_(ry)is plotted by a solid line, and the frequency characteristic F_(fay5) isplotted by a dotted line.

The user input device 504 c has such a configuration that a user canchange the parameters of respective transfer functions G_(fax5)(s) andG_(fay5)(s) such that they have low dimensional degrees by a manualoperation; can instruct the first monitoring unit 504 a to redraw theparameter-changed frequency characteristic F_(fax5); and can instructthe second monitoring unit 504 b to redraw the parameter-changedfrequency characteristic F_(fay5).

Finally, if the user does not manually perform the parameter change, theuser input device 504 c outputs results of the transfer functionsG_(fax5)(s) and G_(fay5) (s) modeled to have a low dimensional degree,which has been first derived by the first monitoring unit 504 a and thesecond monitoring unit 504 b, to the frequency-response display unit504. If the user manually performs the parameter change, the user inputdevice 504 c outputs results of the parameter-changed transfer functionsG_(fax5)(s) and G_(fay5)(s) that are modeled to have a low dimensionaldegree to the frequency-response display unit 504.

The frequency-response display unit 504 outputs the adjustmentparameters for the respective axes to the response-correction-parameterdetermination unit 2 and displays the adjustment parameters thereon onthe basis of the results of the transfer functions G_(fax5)(s) andG_(fay5)(s) modeled to have a low dimensional degree output from theuser input device 504 c. If the user determines that the responsivenesson the X axis needs to be adjusted further, the user input device 504 cis operated to adjust the parameter of the transfer function of the lowdimensional-degree model G_(fay5)(s) on the Y axis. If the userdetermines that the responsiveness of the Y axis needs to be adjustedfurther, the user input device 504 c is operated to adjust the parameterof the transfer function of the low dimensional-degree model G_(fax5)(s)on the X axis.

Due to such a configuration, at the time of adjustment of the responsecorrection parameters on the X axis and the Y axis, if a user wishes toadd further manual adjustment on the basis of the adjustment parameterson the respective axes derived by the frequency-response display unit504, the user can perform a setting operation easily, while confirmingthe change degree of the parameter on a display.

Note that in the present embodiment, the driving system has a two-axisconfiguration, however, the configuration of the driving system is notlimited thereto; can have a multi axes configuration having three ormore axes by using the same method; and may have a plurality of monitorscorresponding thereto.

As described in the first to fifth embodiments, the motor control deviceaccording to the present invention includes a position control unit bymeans of position feedback for each axis; a zero-point estimation unitthat estimates characteristics of a zero point on each axis on the basisof torque commands on the respective axes and a displacement signal of aload machine coupled to a motor; a response-correction-parameterdetermination unit that calculates respective correction filter on eachaxis on the basis of the characteristics of the zero point estimated bythe zero-point estimation unit; and a response correction unit thatinputs a corrected position command converted on the basis of a responsecorrection filter calculated by the response-correction-parameterdetermination unit to each position control unit. Theresponse-correction-parameter determination unit sets the responsecorrection unit for each axis on the basis of the characteristics of thezero point on each axis acquired by the zero-point estimation unit toset the transfer function from a command to a machine end positionidentical on each axis. Accordingly, in the motor control device thatdrives a control target, high acceleration/deceleration driving evenwith a machine having low rigidity can be realized, and it is feasibleto execute trajectory control in which a trajectory drawn by a machineend can follow a command curve without distortion.

INDUSTRIAL APPLICABILITY

As described above, the motor control device according to the presentinvention is useful as a machine tool and a robot in which a controltarget is configured by a low-rigidity mechanical system, and isparticularly suitable as an NC machine tool and an industrial robot.

REFERENCE SIGNS LIST

1 trajectory command generator, 2 response-correction-parameterdetermination unit, 11 X-axis position control unit, 12 X-axis controltarget, 12 a X-axis motor, 12 b X-axis load machine, 12 c X-axisdetector, 13 X-axis response correction unit, 14 X-axis measuringinstrument, 15 X-axis zero-point estimation unit, 16 X-axisexcitation-signal generation unit, 21 Y-axis position control unit, 22Y-axis control target, 22 a Y-axis motor, 22 b Y-axis load machine, 22 cY-axis detector, 23 Y-axis response correction unit, 24 Y-axis measuringinstrument, 25 Y-axis zero-point estimation unit, 26 Y-axisexcitation-signal generation unit, 202 response-correction-parameterdetermination unit, 212 X-axis control target, 212 a X-axis motor, 212 bX-axis load machine, 212 c X-axis detector, 221 Y-axis position controlunit, 301 trajectory command generator, 302response-correction-parameter determination unit, 31 Z-axis positioncontrol unit, 32 Z-axis control target, 32 a Z-axis motor, 32 b Z-axisload machine, 32 c Z-axis detector, 33 Z-axis response correction unit,34 Z-axis measuring instrument, 35 Z-axis zero-point estimation unit, 36Z-axis excitation-signal generation unit, 403 automatic-adjustmentdetermination unit, 415 X-axis zero-point estimation unit, 417 X-axismachine-characteristics analysis unit, 425 Y-axis zero-point estimationunit, 427 Y-axis machine-characteristics analysis unit, 504frequency-response display unit, 504 a first monitoring unit, 504 bsecond monitoring unit, 504 c user input device, T1 X-axis torquecommand, T2 Y-axis torque command, T3 Z-axis torque command, a1 X-axismachine-end displacement signal, a2 Y-axis machine-end displacementsignal, a3 Z-axis machine-end displacement signal.

The invention claimed is:
 1. A motor control device that controls afirst motor coupled to a first load machine in a first control targetand that controls a second motor coupled to a second load machine in asecond control target, the motor control device comprising: a firstdetector to detect a position of the first motor; a second detector todetect a position of the second motor; a trajectory command generator tooutput a first position command that is a position command for the firstcontrol target and a second position command that is a position commandfor the second control target; a first response corrector to carry out acalculation to apply a first response correction filter to the firstposition command from the trajectory command generator so as to output acorrected first position command; a first position controller to receivethe corrected first position command from the first response correctorand a position detected by the first detector so as to generate a firsttorque command such that the position detected by the first detectormatches the corrected first position command; a second positioncontroller to receive the second position command from the trajectorycommand generator and a position detected by the second detector so asto generate a second torque command such that the position detected bythe second detector matches the second position command; a measuringinstrument of the second load machine that detects machine enddisplacement of the second load machine in the second control target; azero-point estimator of the second control target that extractsinformation of a polynomial expression of a transfer functionrepresenting characteristics of a zero point of a transfer function fromthe second torque command to the machine end displacement of the secondload machine, as characteristics of the zero point of the second controltarget, on the basis of the second torque command and the machine enddisplacement of the second control target detected by the measuringinstrument of the second load machine or on the basis of the secondposition command and the machine end displacement of the second controltarget detected by the measuring instrument of the second load machine;and a response-correction-parameter determiner to set the first responsecorrection filter of the first response corrector by using theinformation of the polynomial expression of the transfer functionrepresenting the characteristics of the zero point of the second controltarget extracted by the zero-point estimator of the second controltarget, wherein the first torque command generated by the first positioncontrol unit is input to the first motor, and the second torque commandgenerated by the second position control unit is input to the secondmotor.
 2. The motor control device according to claim 1, furthercomprising: a second response corrector to carry out a calculation toapply a second response correction filter to the second position commandand to output a corrected second position command to the second-positioncontrol unit; a measuring instrument of the first load machine thatdetects machine-end displacement of the first load machine in the firstcontrol target; and a zero-point estimator of the first control targetto extract information of a polynomial expression of a transfer functionrepresenting characteristics of a zero point of a transfer function fromthe first torque command to the machine-end displacement of the firstcontrol target, as characteristics of the zero point of the firstcontrol target, on the basis of the first torque command and the firstmachine-end displacement of the first load machine detected by themeasuring instrument of the first load machine or on the basis of thefirst position command and the first machine-end displacement of thefirst load machine detected by the measuring instrument of the firstload machine, wherein the response-correction-parameter determiner setsthe second response-correction filter of the second response correctorby using the information of the polynomial expression of the transferfunction representing the characteristics of the zero point of the firstcontrol target extracted by the zero-point estimator of the firstcontrol target.
 3. The motor control device according to claim 2,further comprising: a first-axis excitation-signal generator to generatea first excitation signal to be applied to the first torque command forsystem identification; and a second-axis excitation-signal generator togenerate a second excitation signal to be applied to the second torquecommand for system identification, wherein the zero-point estimator ofthe first control target identifies a transfer function from the firstexcitation signal to the first machine end displacement by an inputsignal on the basis of the first excitation signal generated by thefirst-axis excitation-signal generator and on the basis of the machineend displacement of the first load machine so as to extract theinformation of the polynomial expression of the transfer functionrepresenting characteristics of the zero point of the first controltarget, and the zero-point estimator of the second control targetidentifies a transfer function from the second excitation signal to themachine end displacement of the second load machine on the basis of aninput signal on the basis of the second excitation signal generated bythe second-axis excitation-signal generator and on the basis of themachine end displacement of the second load machine so as to extract theinformation of the polynomial expression of the transfer functionrepresenting the characteristics of the zero point of the second controltarget.
 4. The motor control device according to claim 3, furthercomprising: a first machine-characteristics analyzer to obtain firstfrequency characteristics of the first control target on the basis ofthe input signal on the basis of the first excitation signal and on thebasis of the machine end displacement of the first load machine; asecond machine-characteristics analyzer to obtain second frequencycharacteristics of the second control target on the basis of the inputsignal on the basis of the second excitation signal and on the basis ofthe machine end displacement of the second load machine; and anautomatic-adjustment determiner to search for presence of antiresonantcharacteristics of the first control target and the second controltarget respectively on the basis of the first frequency characteristicsobtained by the first machine-characteristics analyzer and the secondfrequency characteristics obtained by the second machine-characteristicsanalyzer, and to determine whether to operate the zero-point estimatorof the first control target and the zero-point estimator of the secondcontrol target, wherein at a time of setting the firstresponse-correction filter and the second response-correction filter,when the automatic-adjustment determiner operates the zero-pointestimator of the first control target, the response-correction-parameterdeterminer sets the second response-correction filter also by using theantiresonant characteristics of the first control target, and when theautomatic-adjustment determiner operates the second-axis zero-pointestimator, the response-correction-parameter determiner sets the firstresponse-correction filter also by using the antiresonantcharacteristics of the second control target.
 5. A motor control devicethat controls a first motor coupled to a first load machine in a firstcontrol target and that controls a second motor coupled to a second loadmachine in a second control target, the motor control device comprising:a first detector to detect a position of the first motor; a seconddetector to detect a position of the second motor; a trajectory commandgenerator to output a first position command that is a position commandfor the first control target and a second position command that is aposition command for the second control target; a first responsecorrector to carry out a calculation to apply a firstresponse-correction filter to the first position command from thetrajectory command generator so as to output a corrected first positioncommand; a first position controller to receive the corrected firstposition command from the first response corrector and the positiondetected by the first detector so as to generate a first torque commandsuch that the position detected by the first detector matches thecorrected first position command; a second response corrector to carryout a calculation to apply a second response-correction filter to thesecond position command from the trajectory command generator so as tooutput a corrected second position command; a second position controllerto receive the corrected second position command from the secondresponse corrector and the position detected by the second detector soas to generate a second torque command such that the position detectedby the second detector matches the corrected second position command; ameasuring instrument of the first load machine that detects machine enddisplacement of the first load machine in the first control target; ameasuring instrument of the second load machine that detects machine enddisplacement of the second load machine in the second control target; afrequency-response display unit that displays frequency characteristicson the basis of the first torque command and machine end displacement ofthe first load machine detected by the measuring instrument of the firstload machine or on the basis of the first position command and the firstmachine end displacement of the first load machine detected by themeasuring instrument of the first load machine, and on the basis of thesecond torque command and the machine end displacement of the secondload machine detected by the measuring instrument of the second loadmachine or on the basis of the second position command and the machineend displacement of the second load machine detected by the measuringinstrument of the second load machine; a first monitor of thefrequency-response display unit to calculate first frequencycharacteristics from the first torque command to the first machine enddisplacement of the first load machine on the basis of the first torquecommand and the machine end displacement of the first load machine or onthe basis of the first position command and the machine end displacementof the first load machine, and to display the first frequencycharacteristics and frequency characteristics of a first simplifiedmodel in which the first frequency characteristics are expressed simplyby a transfer function; a second monitor of the frequency-responsedisplay unit to calculate second frequency characteristics from thesecond torque command to the second machine end displacement of thesecond load machine on the basis of the second torque command and themachine end displacement of the second load machine or on the basis ofthe second position command and the machine end displacement of thesecond load machine, and to display the second frequency characteristicsand frequency characteristics of a second simplified model in which thesecond frequency characteristics are expressed simply by a transferfunction; a user input device of the frequency-response display unitthat performs setting change in a graphical form of the frequencycharacteristics of the first simplified model displayed on the firstmonitor of the frequency-response display unit and the frequencycharacteristics of the second simplified model displayed on the secondmonitor of the frequency-response display unit; and aresponse-correction-parameter determiner to set the firstresponse-correction filter of the first-response corrector and thesecond response-correction filter of the second-response corrector, byusing information of the transfer function of the first simplified modelacquired by the first monitor of the frequency-response display unit andinformation of the transfer function of the second simplified modelacquired by the second monitor of the frequency-response display unit.6. The motor control device according to claim 5, further comprising: afirst-axis excitation-signal generator to generate a first excitationsignal to be applied to the first torque command for systemidentification; and a second-axis excitation-signal generator togenerate a second excitation signal to be applied to the second torquecommand for system identification, wherein the first monitor calculatesthe first frequency characteristics on the basis of the first torquecommand at a time of application of the first excitation signal by thefirst-axis excitation-signal generator and on the basis of the machineend displacement of the first load machine, and displays the firstfrequency characteristics and frequency characteristics of the firstsimplified model in which the first frequency characteristics areexpressed simply by a transfer function, and the second monitorcalculates the second frequency characteristics on the basis of thesecond torque command at a time of application of the second excitationsignal by the second-axis excitation-signal generator and on the basisof the machine end displacement of the second load machine, and displaysthe second frequency characteristics and the frequency characteristicsof the second simplified model in which the second frequencycharacteristics are expressed simply by a transfer function.